Method using manifold system having flow control

ABSTRACT

An injection molding apparatus is provided in which the rate of material flow during the injection cycle is controlled. According to one preferred embodiment, a method is provided for use in an injection molding apparatus including a hot runner assembly comprising a manifold and at least first and second injection nozzles, the hot runner assembly to direct material injected into said manifold through said at least first and second injection nozzles through a corresponding at least first and second gates to one or more mold cavities. The method includes the steps of injecting material into the manifold, controlling, in the hot runner away from the first gate, a first rate at which material is injected through the first gate, and controlling, in the hot runner away from the second gate, a second rate at which material is injected through the second gate, independently from the first rate.

This application is a divisional of application Ser. No. 09/063,762,filed Apr. 21, 1998, entitled MANIFOLD SYSTEM HAVING FLOW CONTROL, andnow pending.

FIELD OF THE INVENTION

This invention relates to injection of pressurized materials through amanifold, such as injection molding of plastic melt in a hot runnersystem. More specifically, this invention relates to an improvedinjection molding hot runner system in which the rate of melt flow iscontrolled through the gate during an injection molding cycle.

DESCRIPTION OF THE RELATED ART

U.S. Pat. No. 5,556,582 discloses a multi-gate single cavity system inwhich the rate of melt flow through the individual gates is controlledindependently via a control system according to specific target processconditions. This system enables the weld line of the part (the sectionof the part in which the melt from one gate meets the melt from anothergate) to be selectively located. It also enables the shape of the weldline to be altered to form a stronger bond.

The '582 patent discloses controlling the rate of melt flow with atapered valve pin at the gate to the mold cavity. It also disclosesplacing a pressure transducer inside the mold cavity. Placing thepressure transducer inside the mold cavity can result in the pressuretransducer sensing pressure spikes which can occur when the valve pin isclosed. A pressure spike sensed by the transducer can cause anunintended response from the control system, and result in a lessprecise control of the melt flow than desired.

The control system disclosed in the '582 patent uses the variables ofvalve pin position and cavity pressure to determine what position thevalve pin should be in. Thus, the algorithm performed by the controlsystem in the '582 patent utilizes two variables to control the rate ofmelt flow into the cavity.

SUMMARY OF THE INVENTION

An injection molding apparatus is provided in which the rate of materialflow during the injection cycle is controlled. According to onepreferred embodiment, a method is provided for use in an injectionmolding apparatus including a hot runner assembly comprising a manifoldand at least first and second injection nozzles, the hot runner assemblyto direct material injected into said manifold through said at leastfirst and second injection nozzles through a corresponding at leastfirst and second gates to one or more mold cavities. The method includesthe steps of injecting material into the manifold, controlling, in thehot runner away from the first gate, a first rate at which material isinjected through the first gate, and controlling, in the hot runner awayfrom the second gate, a second rate at which material is injectedthrough the second gate, independently from the first rate.

According to another embodiment, a method is provided for use in aninjection molding apparatus including a hot runner to direct materialinjected into the hot runner and through a gate and into one or moremold cavities. The method includes the steps of injecting material intothe hot runner assembly, sensing, in the hot runner, a sensed conditionrelated to a rate at which material is injected through the gate, andcontrolling the rate based on said sensed condition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially schematic cross-sectional view of an injectionmolding system according to one embodiment of the present invention;

FIG. 2 is an enlarged fragmentary cross-sectional view of one side ofthe injection molding system of FIG. 1;

FIG. 3 is an enlarged fragmentary cross-sectional view of an alternativeembodiment of a system similar to FIG. 1, in which a plug is used foreasy removal of the valve pin;

FIG. 4 is an enlarged fragmentary cross-sectional view of an alternativeembodiment of a system similar to FIG. 1, in which a threaded nozzle isused;

FIG. 5 is a view similar to FIG. 4, showing an alternative embodiment inwhich a plug is used for easy removal of the valve pin;

FIG. 6 shows a fragmentary cross-sectional view of a system similar toFIG. 1, showing an alternative embodiment in which a forward shut-off isused;

FIG. 7 shows an enlarged fragmentary view of the embodiment of FIG. 6,showing the valve pin in the open and closed positions, respectively;

FIG. 8 is a cross-sectional view of an alternative embodiment of thepresent invention similar to FIG. 6, in which a threaded nozzle is usedwith a plug for easy removal of the valve pin;

FIG. 9 is an enlarged fragmentary view of the embodiment of FIG. 8, inwhich the valve pin is shown in the open and closed positions;

FIG. 10 is an enlarged view of an alternative embodiment of the valvepin, shown in the closed position;

FIG. 11 is a fragmentary cross sectional view of an alternativeembodiment of an injection molding system having flow control thatincludes a valve pin that extends to the gate; and

FIG. 12 is an enlarged fragmentary cross-sectional detail of the flowcontrol area.

DETAILED DESCRIPTION

FIGS. 1-2 show one embodiment of the injection molding system accordingto the present invention. The injection molding system 1 is a multi-gatesingle cavity system in which melt material 3 is injected into a cavity5 from gates 7 and 9. Melt material 3 is injected from an injectionmolding machine 11 through an extended inlet 13 and into a manifold 15.Manifold 15 distributes the melt through channels 17 and 19. Although ahot runner system is shown in which plastic melt is injected, theinvention is applicable to other types of injection systems in which itis useful to control the rate at which a material (e.g., metallic orcomposite materials) is delivered to a cavity.

Melt is distributed by the manifold through channels 17 and 19 and intobores 18 and 20 of nozzles 21 and 23, respectively. Melt is injected outof nozzles 21 and 23 and into cavity 5 (where the part is formed) whichis formed by mold plates 25 and 27. Although a multi-gate single-cavitysystem is shown, the invention is not limited to this type of system,and is also applicable to, for example, multi-cavity systems, asdiscussed in greater detail below.

The injection nozzles 21 and 23 are received in respective wells 28 and29 formed in the mold plate 27. The nozzles 21 and 23 are each seated insupport rings 31 and 33. The support rings serve to align the nozzleswith the gates 7 and 9 and insulate the nozzles from the mold. Themanifold 15 sits atop the rear end of the nozzles and maintains sealingcontact with the nozzles via compression forces exerted on the assemblyby clamps (not shown) of the injection molding machine. An O-ring 36 isprovided to prevent melt leakage between the nozzles and the manifold. Adowel 73 centers the manifold on the mold plate 27. Dowels 32 and 34prevent the nozzle 23 and support ring 33, respectively, from rotatingwith respect to the mold 27.

The nozzles also include a heater 35 (FIG. 2). Although an electric bandheater is shown, other heaters may be used. Furthermore, heat pipes (forexample those disclosed in U.S. Pat. No. 4,389,002) may be disposed ineach nozzle and used alone or in conjunction with heater 35. The heateris used to maintain the melt material at its processing temperature upto the gates 7 and 9. The nozzles 21 and 23 also include an insert 37and a tip 39. The insert can be made of a material (for exampleberyllium copper) having high thermal conductivity in order to maintainthe melt at its processing temperature up to the gate by imparting heatto the melt from the heater 35. The tip 39 is used to form a seal withthe mold plate 27 and is preferably a material (for example titaniumalloy or stainless steel) having low thermal conductivity so as toreduce heat transfer from the nozzle to the mold.

A valve pin 41 having a head 43 is used to control the rate of flow ofthe melt material to the respective gates 7 and 9. The valve pinreciprocates through the manifold. A valve pin bushing 44 is provided toprevent melt from leaking along stem 102 of the valve pin. The valve pinbushing is held in place by a threadably mounted cap 46. The valve pinis opened at the beginning of the injection cycle and closed at the endof the cycle. During the cycle, the valve pin can assume intermediatepositions between the fully open and closed positions, in order todecrease or increase the rate of flow of the melt. The head includes atapered portion 45 that forms a gap 81 with a surface 47 of the bore 19of the manifold. Increasing or decreasing the size of the gap bydisplacing the valve pin correspondingly increases or decreases the flowof melt material to the gate. When the valve pin is closed the taperedportion 45 of the valve pin head contacts and seals with the surface 47of the bore of the manifold.

FIG. 2 shows the head of the valve pin in a Phantom dashed line in theclosed position and a solid line in the fully opened position in whichthe melt is permitted to flow at a maximum rate. To reduce the flow ofmelt, the pin is retracted away from the gate by an actuator 49, tothereby decrease the width of the gap 81 between the valve pin and thebore 19 of the manifold.

The actuator 49 (for example, the type disclosed in U.S. Pat. No.5,894,025) is mounted in a clamp plate 51 which covers the injectionmolding system 1. The actuator 49 is a hydraulic actuator, however,pneumatic or electronic actuators can be used. The actuator 49 includesa hydraulic circuit that includes a movable piston 53 in which the valvepin 41 is threadably mounted at 55. Thus, as the piston 53 moves, thevalve pin 41 moves with it. The actuator 49 includes hydraulic lines 57and 59 which are con trolled by servo valves 1 and 2. Hydraulic line 57is energized to retract the valve pin away from the gate toward theclose position. An actuator cap 61 limits longitudinal movement in thevertical direction of the piston 53. O-rings 63 provide respective sealsto prevent hydraulic fluid from leaking out of the actuator. Theactuator body 65 is mounted to the manifold via screws 67.

A pressure transducer 69 is used to sense the pressure in the manifoldbore 19 downstream of the valve pin head 43. In operation, theconditions sensed by the pressure transducer 69 associated with eachnozzle are fed back to a control system that includes controllers PID 1and PID 2 and a CPU shown schematically in FIG. 1. The CPU executes aPID (proportional, integral, derivative) algorithm which compares thesensed pressure (at a given time) from the pressure transducer to aprogrammed target pressure (for the given time). The CPU instructs thePID controller to adjust the valve pin using the actuator 49 in order tomirror the target pressure for that given time. In this way a programmedtarget pressure profile for an injection cycle for a particular part foreach gate 7 and 9 can be followed.

Although in the disclosed embodiment the sensed condition is pressure,other sensed conditions can be used which relate to melt flow rate. Forexample, the position of the valve pin or the load on the valve pincould be the sensed condition. If so, a position sensor or load sensor,respectively, could be used to feed back the sensed condition to the PIDcontroller. In the same manner as explained above, the CPU would use aPID algorithm to compare the sensed condition to a programmed targetposition profile or load profile for the particular gate to the moldcavity, and adjust the valve pin accordingly.

Melt flow rate is directly related to the pressure sensed in bore 19.Thus, using the controllers PID 1 and PID 2, the rate at which the meltflows into the gates 7 and 9 can be adjusted during a given injectionmolding cycle, according to the desired pressure profile. The pressure(and rate of melt flow) is decreased by retracting the valve pin anddecreasing the width of the gap 81 between the valve pin and themanifold bore, while the pressure (and rate of melt flow) is increasedby displacing the valve pin toward the gate 9, and increasing the widthof the gap 81. The PID controllers adjust the position of the actuatorpiston 51 by sending instructions to servo valves 1 and 2.

By controlling the pressure in a single cavity system (as shown inFIG. 1) it is possible to adjust the location and shape of the weld lineformed when melt flow 75 from gate 7 meets melt flow 77 from gate 9 asdisclosed in U.S. Pat. No. 5,556,582. However, the invention also isuseful in a multi-cavity system. In a multi-cavity system the inventioncan be used to balance fill rates and packing profiles in the respectivecavities. This is useful, for example, when molding a plurality of likeparts in different cavities. In such a system, to achieve a uniformityin the parts, the fill rates and packing profiles of the cavities shouldbe as close to identical as possible. Using the same programmed pressureprofile for each nozzle, unpredictable fill rate variations from cavityto cavity are overcome, and consistently uniform parts are produced fromeach cavity.

Another advantage of the present invention is seen in a multi-cavitysystem in which the nozzles are injecting into cavities which formdifferent sized parts that require different fill rates and packingprofiles. In this case, different pressure profiles can be programmedfor each respective controller of each respective cavity. Still anotheradvantage is when the size of the cavity is constantly changing, i.e.,when making different size parts by changing a mold insert in which thepart is formed. Rather than change the hardware (e.g., the nozzle)involved in order to change the fill rate and packing profile for thenew part, a new program is chosen by the user corresponding to the newpart to be formed.

The embodiment of FIGS. 1 and 2 has the advantage of controlling therate of melt flow away from the gate inside manifold 15 rather than atthe gates 7 and 9. Controlling the melt flow away from the gate enablesthe pressure transducer to be located away from the gate (in FIGS. 1-5).In this way, the pressure transducer does not have to be placed insidethe mold cavity, and is not susceptible to pressure spikes which canoccur when the pressure transducer is located in the mold cavity or nearthe gate. Pressure spikes in the mold cavity result from the valve pinbeing closed at the gate. This pressure spike could cause an unintendedresponse from the control system, for example, an opening of the valvepin to reduce the pressure—when the valve pin should be closed.

Avoidance of the effects of a pressure spike resulting from closing thegate to the mold makes the control system behave more accurately andpredictably. Controlling flow away from the gate enables accuratecontrol using only a single sensed condition (e.g., pressure) as avariable. The '582 patent disclosed the use of two sensed conditions(valve position and pressure) to compensate for an unintended responsefrom the pressure spike. Sensing two conditions resulted in a morecomplex control algorithm (which used two variables) and morecomplicated hardware (pressure and position sensors).

Another advantage of controlling the melt flow away from the gate is theuse of a larger valve pin head 43 than would be used if the valve pinclosed at the gate. A larger valve pin head can be used because it isdisposed in the manifold in which the melt flow bore 19 can be madelarger to accommodate the larger valve pin head. It is generallyundesirable to accommodate a large size valve pin head in the gate areawithin the end of the nozzle 23, tip 39 and insert 37. This is becausethe increased size of the nozzle, tip and insert in the gate area couldinterfere with the construction of the mold, for example, the placementof water lines within the mold which are preferably located close to thegate. Thus, a larger valve pin head can be accommodated away from thegate.

The use of a larger valve pin head enables the use of a larger surface45 on the valve pin head and a larger surface 47 on the bore to form thecontrol gap 81. The more “control” surface (45 and 47) and the longerthe “control” gap (81)—the more precise control of the melt flow rateand pressure can be obtained because the rate of change of melt flow permovement of the valve pin is less. In FIGS. 1-3 the size of the gap andthe rate of melt flow is adjusted by adjusting the width of the gap,however, adjusting the size of the gap and the rate of material flow canalso be accomplished by changing the length of the gap, i.e., the longerthe gap the more flow is restricted. Thus, changing the size of the gapand controlling the rate of material flow can be accomplished bychanging the length or width of the gap.

The valve pin head includes a middle section 83 and a forward coneshaped section 95 which tapers from the middle section to a point 85.This shape assists in facilitating uniform melt flow when the melt flowspast the control gap 81. The shape of the valve pin also helpseliminates dead spots in the melt flow downstream of the gap 81.

FIG. 3 shows another aspect in which a plug 87 is inserted in themanifold 15 and held in place by a cap 89. A dowel 86 keeps the plugfrom rotating in the recess of the manifold that the plug is mounted.The plug enables easy removal of the valve pin 41 without disassemblingthe manifold, nozzles and mold. When the plug is removed from themanifold, the valve pin can be pulled out of the manifold where the plugwas seated since the diameter of the recess in the manifold that theplug was in is greater than the diameter of the valve pin head at itswidest point. Thus, the valve pin can be easily replaced withoutsignificant downtime.

FIGS. 4 and 5 show additional alternative embodiments of the inventionin which a threaded nozzle style is used instead of a support ringnozzle style. In the threaded nozzle style, the nozzle 23 is threadeddirectly into manifold 15 via threads 91. Also, a coil heater 93 is usedinstead of the band heater shown in FIGS. 1-3. The threaded nozzle styleis advantageous in that it permits removal of the manifold and nozzles(21 and 23) as a unitary element. There is also less of a possibility ofmelt leakage where the nozzle is threaded on the manifold. The supportring style (FIGS. 1-3) is advantageous in that one does not need to waitfor the manifold to cool in order to separate the manifold from thenozzles. FIG. 5 also shows the use of the plug 87 for convenient removalof valve pin 41.

FIGS. 6-10 show an alternative embodiment of the invention in which a“forward” shutoff is used rather than a retracted shutoff as shown inFIGS. 1-5. In the embodiment of FIGS. 6 and 7, the forward cone-shapedtapered portion 95 of the valve pin head 43 is used to control the flowof melt with surface 97 of the inner bore 20 of nozzle 23. An advantageof this arrangement is that the valve pin stem 102 does not restrict theflow of melt as in FIGS. 1-5. As seen in FIGS. 1-5, the clearance 100between the stem 102 and the bore 19 of the manifold is not as great asthe clearance 100 in FIGS. 6 and 7. The increased clearance 100 in FIGS.6-7 results in a lesser pressure drop and less shear on the plastic.

In FIGS. 6 and 7 the control gap 98 is formed by the front cone-shapedportion 95 and the surface 97 of the bore 20 of the rear end of thenozzle 23. The pressure transducer 69 is located downstream of thecontrol gap—thus, in FIGS. 6 and 7, the nozzle is machined toaccommodate the pressure transducer as opposed to the pressuretransducer being mounted in the manifold as in FIGS. 1-5.

FIG. 7 shows the valve pin in solid lines in the open position andPhantom dashed lines in the closed position. To restrict the melt flowand thereby reduce the melt pressure, the valve pin is moved forwardfrom the open position towards surface 97 of the bore 20 of the nozzlewhich reduces the width of the control gap 98. To increase the flow ofmelt the valve pin is retracted to increase the size of the gap 98.

The rear 45 of the valve pin head 43 remains tapered at an angle fromthe stem 102 of the valve pin 41. Although the surface 45 performs nosealing function in this embodiment, it is still tapered from the stemto facilitate even melt flow and reduce dead spots.

As in FIGS. 1-5, pressure readings are fed back to the control system(CPU and PID controller), which can accordingly adjust the position ofthe valve pin 41 to follow a target pressure profile. The forwardshut-off arrangement shown in FIGS. 6 and 7 also has the advantages ofthe embodiment shown in FIGS. 1-5 in that a large valve pin head 43 isused to create a long control gap 98 and a large control surface 97. Asstated above, a longer control gap and greater control surface providesmore precise control of the pressure and melt flow rate.

FIGS. 8 and 9 show a forward shutoff arrangement similar to FIGS. 6 and7, but instead of shutting off at the rear of the nozzle 23, theshut-off is located in the manifold at surface 101. Thus, in theembodiment shown in FIGS. 8 and 9, a conventional threaded nozzle 23 maybe used with a manifold 15, since the manifold is machined toaccommodate the pressure transducer 69 as in FIGS. 1-5. A spacer 88 isprovided to insulate the manifold from the mold. This embodiment alsoincludes a plug 87 for easy removal of the valve pin head 43.

FIG. 10 shows an alternative embodiment of the invention in which aforward shutoff valve pin head is shown as used in FIGS. 6-9. However,in this embodiment, the forward cone-shaped taper 95 on the valve pinincludes a raised section 103 and a recessed section 104. Ridge 105shows where the raised portion begins and the recessed section ends.Thus, a gap 107 remains between the bore 20 of the nozzle through whichthe melt flows and the surface of the valve pin head when the valve pinis in the closed position. Thus, a much smaller surface 109 is used toseal and close the valve pin. The gap 107 has the advantage in that itassists opening of the valve pin which is subjected to a substantialforce F from the melt when the injection machine begins an injectioncycle. When injection begins melt will flow into gap 107 and provide aforce component F1 that assists the actuator in retracting and openingthe valve pin. Thus, a smaller actuator, or the same actuator with lesshydraulic pressure applied, can be used because it does not need togenerate as much force in retracting the valve pin. Further, the stressforces on the head of the valve pin are reduced.

Despite the fact that the gap 107 performs no sealing function, itswidth is small enough to act as a control gap when the valve pin is openand correspondingly adjust the melt flow pressure with precision as inthe embodiments of FIGS. 1-9.

FIGS. 11 and 12 show an alternative hot-runner system having flowcontrol in which the control of melt flow is still away from the gate asin previous embodiments. Use of the pressure transducer 69 and PIDcontrol system is the same as in previous embodiments. In thisembodiment, however, the valve pin 41 extends past the area of flowcontrol via extension 110 to the gate. The valve pin is shown in solidlines in the fully open position and in Phantom dashed lines in theclosed position. In addition to the flow control advantages away fromthe gate described above, the extended valve pin has the advantage ofshutting off flow at the gate with a tapered end 112 of the valve pin41.

Extending the valve pin to close the gate has several advantages. First,it shortens injection cycle time. In previous embodiments thermal gatingis used. In thermal gating, plastication does not begin until the partfrom the previous cycle is ejected from the cavity. This preventsmaterial from exiting the gate when the part is being ejected. Whenusing a valve pin, however, plastication can be performed simultaneouslywith the opening of the mold when the valve pin is closed, thusshortening cycle time by beginning plastication sooner. Using a valvepin can also result in a smoother gate surface on the part.

The flow control area is shown enlarged in FIG. 12. In solid lines thevalve pin is shown in the fully open position in which maximum melt flowis permitted. The valve pin includes a convex surface 114 that tapersfrom edge 128 of the stem 102 of the valve pin 41 to a throat area 116of reduced diameter. From throat area 116, the valve pin expands indiameter in section 118 to the extension 110 which extends in a uniformdiameter to the tapered end of the valve pin.

In the flow control area the manifold includes a first section definedby a surface 120 that tapers to a section of reduced diameter defined bysurface 122. From the section of reduced diameter the manifold channelthen expands in diameter in a section defined by surface 124 to anoutlet of the manifold 126 that communicates with the bore of the nozzle20. FIGS. 11 and 12 show the support ring style nozzle similar to FIGS.1-3. However, other types of nozzles may be used such as, for example, athreaded nozzle as shown in FIG. 8.

As stated above, the valve pin is shown in the fully opened position insolid lines. In FIG. 12, flow control is achieved and melt flow reducedby moving the valve pin 41 forward toward the gate thereby reducing thewidth of the control gap 98. Thus, surface 114 approaches surface 120 ofthe manifold to reduce the width of the control gap and reduce the rateof melt flow through the manifold to the gate.

To prevent melt flow from the manifold bore 19, and end the injectioncycle, the valve pin is moved forward so that edge 128 of the valve pin,i.e., where the stem 102 meets the beginning of curved surface 114, willmove past point 130 which is the beginning of surface 122 that definesthe section of reduced diameter of the manifold bore 19. When edge 128extends past point 130 of the manifold bore melt flow is prevented sincethe surface of the valve stem 102 seals with surface 122 of themanifold. The valve pin is shown in dashed lines where edge 128 isforward enough to form a seal with surface 122. At this position,however, the valve pin is not yet closed at the gate. To close the gatethe valve pin moves further forward, with the surface of the stem 102moving further along, and continuing to seal with, surface 122 of themanifold until the end 112 of the valve pin closes with the gate.

In this way, the valve pin does not need to be machined to close thegate and the flow bore 19 of the manifold simultaneously, since stem 102forms a seal with surface 122 before the gate is closed. Further,because the valve pin is closed after the seal is formed in themanifold, the valve pin closure will not create any unwanted pressurespikes. Likewise, when the valve pin is opened at the gate, the end 112of the valve pin will not interfere with melt flow, since once the valvepin is retracted enough to permit melt flow through gap 98, the valvepin end 112 is a predetermined distance from the gate. The valve pincan, for example, travel 6 mm. from the fully open position to where aseal is first created between stem 102 and surface 122, and another 6mm. to close the gate. Thus, the valve pin would have 12 mm. of travel,6 mm. for flow control, and 6 mm. with the flow prevented to close thegate. Of course, the invention is not limited to this range of travelfor the valve pin, and other dimensions can be used.

Having thus described certain embodiments of the present invention,various alterations, modifications, and improvements will readily occurto those skilled in the art. Such alterations, modifications, andimprovements are intended to be within the spirit and scope of theinvention. Accordingly, the foregoing description is by way of exampleonly, and not intended to be limiting. The invention is limited only asdefined in the following claims and the equivalents thereof.

What is claimed is:
 1. In an injection molding apparatus including amanifold and at least first and second injection nozzles, the apparatusto direct material injected into said manifold through said at leastfirst and second injection nozzles through a corresponding at leastfirst and second gates to one or more mold cavities, a method comprisingsteps of: (A) injecting material into the manifold; (B) altering, in theapparatus away from the first gate and during an injection cycle, afirst rate at which material is injected through the first gate; and (C)altering, in the apparatus away from the second gate and during aninjection cycle, a second rate at which material is injected through thesecond gate, independently from the first rate.
 2. The method of claim1, wherein the first and second rates are altered in the manifold. 3.The method of claim 1, wherein the first and second rates are altered inthe first and second nozzles, respectively.
 4. The method of claim 3,wherein the first and second rates are altered at a rearward end of eachof the first and second nozzles, respectively.
 5. The method of claim 1,wherein altering the first rate is based on a first sensed conditionrelated to the rate of material flow through the first gate, andaltering the second rate is based on a second sensed condition relatedto the rate of material flow through the second gate.
 6. The method ofclaim 5, wherein altering the first rate is based only on the firstsensed condition, and altering the second rate is based only on thesecond sensed condition.
 7. The method of claim 5, wherein the sensedcondition is pressure.
 8. The method of claim 1, wherein step (B)includes altering a size of a first pathway in the apparatus throughwhich the material flows to alter the first rate, and step (C) includesaltering a size of a second pathway in the apparatus through which thematerial flows to alter the second rate.
 9. The method of claim 8,wherein the first and second pathways are in the manifold.
 10. Themethod of claim 5, wherein the first rate is altered based on a resultof a comparison of the first sensed condition to a first target value ofthe first sensed condition, and the second rate is altered based on aresult of a comparison of the second sensed condition to a second targetvalue of the second sensed condition.
 11. The method of claim 10,further comprising altering the first and second rates so that the firstand second sensed conditions track the first and second target valuesthroughout an injection cycle.
 12. The method of claim 1, wherein thefirst rate differs from the second rate during at least of portion of aninjection cycle.
 13. The method of claim 10, wherein the first andsecond target values differ from one another.
 14. The method of claim10, wherein the first and second sensed conditions are materialpressure.
 15. The method of claim 8, wherein the first and secondpathways are in a rearward end of the first and second nozzles.
 16. Themethod of claim 10, wherein the first and second target values are thesame.
 17. The method of claim 5, wherein the first and second sensedconditions are sensed in the apparatus.
 18. The method of claim 17,wherein the first and second sensed conditions are sensed in the firstand second injection nozzles, respectively.
 19. The method of claim 17,wherein the first and second sensed conditions are sensed in themanifold.
 20. The method of claim 5, further comprising independentlyadjusting the first and second rates throughout an injection cycle basedon the first and second sensed conditions, respectively.
 21. The methodof claim 1, further comprising altering the first and second ratesduring the injection cycle to track target conditions indicative of therespective magnitudes of the first and second rates.
 22. The method ofclaim 21, wherein the first and second rates are altered in one of theinjection nozzles and the manifold.
 23. The method of claim 1, whereinthe first and second rates are altered during the injection cycle inresponse to a comparison of first and second sensed conditions relatedto the first and second rates at which material is injected through thefirst and second gates, respectively, to first and second target valuesof the first and second sensed conditions.
 24. The method of claim 23,wherein the first and second rates are altered in one of the injectionnozzles and the manifold.
 25. In an injection molding apparatusincluding a manifold and at least first and second injection nozzles todirect material injected into the manifold and at least first and secondinjection nozzles and through at least first and second gates incommunication therewith and into one or more mold cavities, a methodcomprising the steps of: (A) injecting material into the manifold andthe first and second injection nozzles; (B) sensing, in at least one ofthe manifold and the first injection nozzle, a first sensed conditionrelated to a first rate at which material is injected through the firstgate; (C) altering the first rate during an injection cycle based onsaid first sensed condition; (D) sensing, in at least one of themanifold and the second injection nozzle, a second sensed conditionrelated to a second rate at which material is injected through thesecond gate and into said one or more mold cavities; and (E) alteringthe second rate during the injection cycle based on said second sensedcondition.
 26. The method of claim 25, wherein the first or second rateis altered in at least one of the manifold and the first and secondinjection nozzles.
 27. The method of claim 25, wherein the first rate isaltered independently from the second rate.
 28. The method of claim 25,wherein the first and second rates are altered as a result of acomparison of the first and second sensed conditions to first and secondtarget values of the first and second sensed conditions, respectively.29. The method of claim 25, wherein the first and second rates arealtered in the manifold.
 30. The method of claim 25, wherein step (C)includes altering a size of a first pathway in at least one of themanifold and the first injection nozzle through which the material flowsto alter the first rate, and step (E) includes altering a size of asecond pathway in at least one of the manifold and the second injectionnozzle through which the material flows to alter the second rate. 31.The method of claim 28, further comprising altering the first and secondrates so that the first and second sensed conditions track the first andsecond target values throughout an injection cycle.
 32. The method ofclaim 25, further comprising independently adjusting the first andsecond rates throughout an injection cycle based on the first and secondsensed conditions, respectively.